The present invention relates to improvements in wear surfaces for the trucks of railroad locomotives. More particularly, the invention relates to an improved bearing system between those portions of such trucks, which are slidably disposed to one another to enable the wheels and the body of the vehicle to move relative to each other in a vertical direction, while providing horizontal containment for the wheel axle.
A conventional locomotive is supported on a truck, which is composed of a single casting with integral pedestal jaws, that are spaced apart and connected together by a transverse member. This type of truck is often referred to as a pedestal truck. The pedestals are part of the jaws and form inverted U-shaped sections so a journal box at each end of the wheel axle can be received between the legs of the jaws, suspending a journal box therebetween on each side the truck, so each box can move vertically in relationship to the truck, while being retained against horizontal displacement. These trucks may contain up to three sets of jaws. Rubbing contact between the vertical surfaces of each box and its contiguous legs of the jaws results from this arrangement.
Two downwardly facing fingers on truck the form an inverted U, which are called the pedestal legs and the space between them is the open jaw. Each truck has two open jaws, or a set of jaws, and may have up to three sets of open jaws. Each open jaw is closed at its bottom by a pedestal tie bar after the journal box is received in the open jaw. In this manner, the journal boxes are positioned within the open jaws in a vertical sliding relationship within the truck. As the locomotive body is supported by the truck assembly, this arrangement allows vertical movement between the locomotive body and the journal boxes on which the wheels are mounted, and which have springs between the boxes and the truck.
Rapid wear occurs at the vertical interfaces between the pedestal legs and each journal box, due to the high horizontal loadings under acceleration and deceleration. Thus, wear plates are normally attached to one or more of the opposing faces on the pedestal legs and journal boxes to reduce the wear and protect the underlying parts. The wear plates attached to the pedestal legs are commonly referred to as pedestal liners and are the subject matter of the present invention.
Originally the pedestal liners were made of hardened steel. More recently they have been made from thermoplastics, such as nylon, because such materials last much longer than the hardened steel components previously used.
One pedestal liner, shaped like the original steel liner, now in use, is produced by a monolithic nylon casting process. However, the resulting castings proved less serviceable than injection molded pedestal liners because they have minimal shock absorbing properties, coupled with a high breakage rate. Cast liners of this type are disclosed in U.S. Pat. No. 3,554,618 to Ditzler et al.
Ditzler also obtained U.S. Pat. No. 4,094,253 on a floating pedestal liner constructed of cast nylon. This liner design has no attachment to its associated pedestal leg, allowing it to float on both the pedestal leg and on the wear surface of the journal box. Ostensibly due to the movement of the loose or floating liner between the legs and the journal box, this design has a low longevity. As a result, this design was not generally adopted by the railroad industry.
In Houston's U.S. Pat. No. 4,170,180, spacing washers are employed with bolts used to attach nylon pedestal liners to the pedestal legs. These washers are designed to limit the amount of compression placed on the nylon liner by the attaching bolts, thereby preventing cold flow of the nylon in the liner, due to the compression thereof by the attaching bolts.
Such cold flow often causes the liner's wear surface to move away from the faces of the pedestal leg, resulting in poor liner performance and breakage, because of a resulting gap between the pedestal liner and the pedestal leg. Typically a space of about one-sixteenth of an inch is common when cold flow occurs in nylon liners without the spacing washers, such a gap, as well as larger ones, reduce the service life for the pedestal liner. It is also believed that impact abrasion occurs on the surface supporting the liner, and is increased when gaps exists between the liner and the leg face, damaging the face of the leg. Further, misaligned bolt holes may also contribute to the gap between these parts.
While the liners built according to U.S. Pat. No. 4,170,180 provide a superior wear plate, a problem still exists with all nylon pedestal liners due to concentrated localized loading, on the their edges, such as occurs when a locomotive negotiates a tight curve in the tracks. Since the wheels on the axle are fixedly joined together, the difference in wheel travel of the inside wheel in relation to the outside wheel during travel around a curve will move one journal box forward and the other rearward relative to the jaw. As a small gap exists between the pedestal liner and the wear face on the journal boxes, the axle will skew enough to substantially increase the edge load on the outside edges of the liners, during these conditions.
Maintenance records indicate locomotives having twisting track systems (many tight curves) obtain a much shorter service life from thermoplastic pedestal liners. This is a problem addressed by the novel system of this invention which, under experimental test, shows a substantial increase in service life, even under the most extreme operating conditions.